Bioassay-guided fractionation of the acid hydrolysate of total ginsenosides of Panax ginseng C.A.Meyer (Araliaceae) led to the isolation of a novel ginsengenin(1).The structure of 1 was determined as (20S,22S)-dammar-22,25-epoxy-3β,12β,20-triol by extensive spectroscopy and single-crystal X-ray diffraction analyses.The cytotoxicity of 1 was further tested against SWl 116,HCTl 16,and A549 cells by the MTT method,with IC_(50) values in the range of 2.96-30.9μmol/L. Bioassay-guided fractionation of the acid hydrolysate of total ginsenosides of Panax ginseng CAMeyer (Araliaceae) led to the isolation of a novel ginsengenin (1). The structure of 1 was determined as (20S, 22S) -dammar-22, 25- epoxy-3β, 12β, 20-triol by extensive spectroscopy and single-crystal X-ray analysis of the cytotoxicity of 1 was further tested against SW1 116, HCT1 16, and A549 cells by the MTT method, with IC_ (50) values in the range of 2.96-30.9 μmol / L.